Rare earth elements, known as the “vitamin” of industry, are key materials used in many electronic products and weapon systems. Because of numerous components of a rare earth material and very similar properties of rare earth elements, cascade extraction is usually used in the industrial production of rare earth to complete separation of elements in the rare earth material. In order to obtain single high-purity rare earth elements, a mixer-settler used in rare earth extraction and separation sometimes is provided with hundreds of stages, and element components between adjacent stages change little in content and easily generate strong coupling. As a result, there is obvious hysteresis of control strategy adjustment and it is difficult to perform control in real time. If component content of elements of an export product is not within a production requirement, the elements of the export product need to be extracted again, leading to a great waste of manpower, material resources, and time.
In current practice, in-situ sampling and off-line detection in a laboratory are mainly used to obtain information about component content of rare earth elements. However, a rare earth solvent extraction is a continuous process, and consequently the off-line detection method cannot accurately reflect a real situation in real time. Many enterprises use online detection methods, such as a spectrophotometric method and a ray analysis method. A spectrophotometer and an optical fiber reflection probe are combined in detection based on the spectrophotometric method, and during the detection, the probe is inserted into a mixer-settler, and the spectrophotometer scans the probe and reflects light to implement the detection of component content of elements in rare earth mixed liquid. This method requires an operator to perform an actual operation at an extraction site, and therefore there is a specific delay. As a result, there is a problem of a detection delay in the spectrophotometric method. In the ray analysis method, a Compton scattering principle is mainly used, and a detection instrument performs online detection of component content of rare earth elements in an extraction process. This ray analysis method can only be used for single detection, and therefore cannot perform continuous detection. Thus, the existing detection methods have a problem of not being able to perform continuous detection in real time.